build: scan.mk: consider KernelPackage pattern as well

The removal of the ".+Package" pattern in scan.mk also caused the build
system to skip over Makefiles defining only kmods. Adjust the grep pattern
to consider packages with "call KernelPackage" signatures as well.

Signed-off-by: Jo-Philipp Wich <[email protected]>

include/scan.mk

@@ -51,7 +51,7 @@ $(OVERRIDELIST):
 ifeq ($(SCAN_NAME),target)
   GREP_STRING=BuildTarget
 else
-  GREP_STRING=(Build/DefaultTargets|BuildPackage)
+  GREP_STRING=(Build/DefaultTargets|BuildPackage|KernelPackage)
 endif
 
 $(FILELIST): $(OVERRIDELIST)